Field of the Invention
The present disclosure relates generally to electrical storage batteries and, in particular, to battery packs having a plurality of rechargeable cells electrically coupled to each other and to a control circuit disposed within a common housing. In particular, the present disclosure relates to a plurality of lithium ion cells arranged according to an improved internal packing configuration. These cells, and additional components such as a control circuit, are disposed within a housing, such as a housing of conventional size and design.
Description of the Related Art
There has been interest in the electrical power supply industry to provide rechargeable battery systems having a compact, lightweight construction made with relatively inexpensive components such as readily commercially available individual storage cells coupled together and operating under the control of one or more control circuits so as to provide advanced functions such as fuel gauging, cell balancing, and communication via a serial data communications bus.
In addition to battery capacity needed to drive the intended load, demands arise from the nature of the application and the intended use of the load and battery system. An example of one particularly challenging field of use is that of modern rugged mobile military applications. Military applications now demand higher performance, lower weight, longer effective usage times, and high reliability for mobile, handheld applications such as navigation, fire control, and Multiband Inter/Intra Team Radios (MBITR). These systems rely on increasingly sophisticated battery packs for their power requirements, yet they present unique design challenges because of the extreme environments to which they are exposed. Design engineers are faced with an array of challenges in developing effective battery systems—from cell and cell pack selection to intelligent power management, and from safety concerns to charging systems. For example, should the battery system undergo full or partial power failure, a command signal may change state in an unexpected and undesired manner. Armed with an understanding of these demands, however, designers can make the best choices for battery-supplied power in modern rugged military applications.
Without a simple and cost-effective charging system coupled with reliable rechargeable battery chemistry, the significance of portable lightweight battery energy sources would drop as a practical reality and have a far less impact on modern technology. Handheld radios, telemetry monitors, weather stations, test equipment, missiles, rockets, satellites, and a myriad of other equipment all rely on cost-effective reliable rechargeable battery technology for their operation. Indeed, without practical rechargeable battery systems, devices would be too cumbersome in their operation for everyday use.
Arguably, the most promising widespread rechargeable battery technology in use today is lithium ion technology. This battery chemistry technology was first discovered in 1912 and the first lithium batteries were proposed around 1970. As is true in many other disciplines, substantial advancements in the technology were not made until new materials with superior performance characteristics were developed. Today, lithium ion technology takes many forms. Perhaps the greatest and most promising form is that of lithium cobalt oxide (Li-cobalt), but lithium manganese oxide (Li-manganese), lithium iron phosphate (Li-phosphate), lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA) and lithium titanate (Li-titanate) also play a substantial, commercially significant role.
Lithium ion (Li-ion) cell characteristics include a nominal voltage of 3.6 V, 1000 duty cycles per lifetime, a rate load current of less than 4 C, an average energy density of 160 Wh/kg, a charge time of less than 4 hours, and a typical discharge rate of a few percent per month when in storage. Li-ion cells operate effectively between −20° C. and 60° C. With recent improvements in battery chemistry, most notably new chemical formulations, the range is extended from −30° C. to 80° C.
Principally, three primary components come together to form a lithium-ion cell. These include a positive electrode or cathode, made from a layered metal oxide such as lithium cobalt oxide, a polyanion such as lithium iron phosphate, or a spinel such as lithium manganese oxide. Also included is a negative electrode or anode made, for example, from carbon, graphite, or the like. An electrolyte surrounds the electrodes and may comprise, for example, a lithium salt suspended in an organic solvent. Examples of electrolytes also include mixtures of organic carbonates such as ethylene carbonate or diethyl carbonate. Since pure lithium is highly reactive, battery designers frequently opt to use a non-aqueous electrolyte. Of importance here is the recognition that these various material types making up a lithium ion cell must be compatible with one another and when combined in a battery system, the voltage, capacity, operational life, and operational safety of the resulting lithium-ion battery can take on a wide variety of values. Typically, the electrodes and electrolyte are protected by an outer container sealed to prevent the intrusion of water. Compared to other battery chemistries, lithium-ion battery systems require careful control in their operation to limit peak voltages and to prevent a wide array of damage to the battery system.
After construction, a lithium-ion cell must be charged in order to acquire energy which is stored in the battery for later use. When the battery is being charged, lithium ions are liberated from the positive electrode and move through the electrolyte to the negative electrode where they remain. During discharge, the lithium ions move in the reverse direction across the electrolyte toward the positive electrode, producing energy for an external device through electron flow through the device, a process interconnected to that of ion flow within the cell.
As will be seen herein, the present disclosure describes an application with lithium-ion cells having a cylindrical form. However, as will be appreciated from studying the materials herein, the present disclosure also describes practical applications using other shapes or formats of lithium-ion cells, including those having a soft flat body or pouch, as well as larger cylindrical shapes which include terminals affording ready mechanical connection to external devices.
As mentioned, the present disclosure describes uses of lithium ion technology with rechargeable battery systems. However, in the field of lithium ion technology, these types of systems all have a limited thermal operating range. At times, it is necessary to provide portable lightweight electrical power in environments having extreme temperature ranges. A classic solution to overcome this type of problem has been to use non-rechargeable battery systems, typically referred to as primary lithium battery systems. The present disclosure is also relevant to non-rechargeable or primary battery systems. In extreme applications, rechargeable battery chemistries may not be able to perform in a reliable manner. In this instance, disposable, one-time-use lithium cells (known as lithium-primary cells) may be considered. These lithium-primary cells feature a nominal voltage of 3.6 V, an optimal load current of less than 5 C, an average energy density of 160 Wh/kg and a negligible self-discharge rate supporting years of storage.
The range of anticipated operating temperatures often lies at the heart of extreme applications. By way of example, lithium-primary cells have been known to operate in temperatures ranging from −40° C. to +80° C. Examples of lithium-primary chemistries include lithium thionyl chloride (Li/SOCl2), lithium sulfur dioxide (Li/SO2), and lithium manganese dioxide (Li/MnO2).
Although the present disclosure discusses a wide array of lithium-ion technologies, it applies equally well to different types of battery chemistries, employing materials unrelated to those of lithium-ion systems. As will be seen herein, in one aspect, the present disclosure is directed to systems of battery packs, which employ a plurality of individual cells physically associated together and electrically coupled together to operate as a single entity. Thus, the present disclosure is concerned with balancing the compatibilities among all of the components employed within the systems, despite the precise nature of any particular system. Such considerations will come to the fore when considering the development of control circuitry designed to protect the system as a whole as well as to provide balance among its various components so as to optimize overall system performance.
One ongoing challenge has been to offer greater battery capacities in ever smaller sized packages. A special example of this industry goal is to provide increases in energy capacity for conventional, standardized packages that are well defined in the industry. Battery systems are not readily miniaturized using photolithographic and other popular techniques, as may be possible with other electronics components. Rather, reductions in battery size are more usually accompanied by improvements in battery materials to enable greater energy storage in a smaller sized package. This of course may be accompanied by changes in battery chemistry. The present disclosures describes advantages of increasing the capacity of battery packs, regardless of any particular chemistry employed or whether the battery cells are rechargeable.
Approaching the problem from a different perspective, there remains a need to adapt and improve upon known commercial products to reduce overall operating expenses by eliminating the need for additional training of end-users and maintenance technicians. A special example of this is in the realm of military applications, where familiarity with new, improved products is vital to mission success, where lives are placed at risk in the interest of national defense. As is well known to those employed in the battlefield, it is surprising how quickly even very small changes can spin out of control in a critical, life-threatening situation. Reducing complexity and increasing familiarity with systems allows greater attention to be directed to the task at hand.
Apart from using known systems in a known way, it is frequently necessary to adapt or customize a system to meet changing conditions. By reducing the need to pay attention to changes in standardized systems, a user can devote greater energy to adapting a given system to meet unusual, unforeseen requirements. As a related benefit, by keeping improvements in existing equipment transparent to the user, greater use can be made of related accessories. As those responsible for systems operation will attest, oftentimes the array of accessories can outweigh the system they support.
As with other types of electronic components, battery systems are becoming more sophisticated and have a tendency to use newer materials that exhibit sensitivities and requirements not previously encountered. With the ability to apply increasingly complex electronic controls, materials and component arrangements that are more inherently unstable may be made reliable in a practical environment. Nonetheless, the overall package must, as always, be rugged and capable of withstanding harsh environmental conditions. Controls needed to maintain a high standard of systems reliability must however not be prohibitively expensive or unusually difficult to deploy in practical real-world products. As will be seen herein, the present disclosure describes these desired types of improvements, thus delivering advantages without unnecessary downside risk.
As systems managers will immediately appreciate, substantial cost advantages can be achieved whenever a system can be constructed from a smaller variety of different types of components. For example, inventory costs are reduced, and critical components are easier to stock and are more readily obtained in the available marketplace. In addition, training costs are reduced, and it is more likely that peripheral knowledge and skills developed for similar but not identical products can be brought to bear for products being designed and deployed. As a result, design times for new products can be greatly reduced. The present disclosure describes such advantages and simplified construction of the battery packs and other battery systems.
Despite numerous advances, there remains a need for relatively simple, durable devices to provide portable and lightweight electrical energy sources.